1. Technical Field
The invention relates to an image capturing device and an image processing method thereof. Particularly, the invention relates to an image processing method capable of blending images by calculating pixel gradients.
2. Related Art
Along with development of optical technology, digital cameras capable of adjusting aperture, shutter and even changing lenses are widely used, and functions of the digital camera tend to be diversified. Besides that the digital camera is required to provide good imaging quality, accuracy and speed of a focusing technique are also factors considered by a consumer when the consumer purchases the digital camera. However, regarding an existing optical system, since different objects have different distances in a three-dimensional scene, an entirely clear full depth of field (DOF) image cannot be obtained in a single image capturing process. Namely, limited by a lens optical characteristic, when the digital camera is used to capture image, only one of depths is selected for focusing, so that objects of other depths in the image are less clear.
A conventional method of producing a full DOF image is to combine a plurality of images captured according to different capturing conditions. Different images of one scene are captured by changing one or a plurality of parameters in the capturing condition, and these images are combined into one clear image according to a clarity determination method. The technique of capturing images according to the above different capturing conditions to produce the full DOF image relies on a fixed image capturing device. Generally, a user usually uses a stable tripod to fix the image capturing device, so as to ensure that the captured images have none obvious geometric distortion there between. Moreover, during the image capturing process, movement of any object in the scene to be captured has to be avoided as well.
On the other hand, when the camera is used to capture images, in order to highlight a theme of the captured image, an image capturing technique of “bokeh” is generally adopted. The so-called “bokeh” refers to that in a captured image with a shallow DOF, the part of image outside the DOF gradually produces a loose blur effect. Generally, a bokeh effect produced by the camera lens is limited. In order to obtain a better bokeh effect, important conditions of large aperture and long focal length have to be satisfied. In other words, in order to achieve a better bokeh effect, a large aperture lens is used to strengthen blur of distant objects, so as to highlight the clear theme from the background. However, the large aperture lens has a large volume and high cost, which is not suitable for the general consumable cameras.
Therefore, the conventional method for producing the full DOF image or the dokeh image is liable to cause a problem that the processed image has a discontinuous DOF or unnatural result. Moreover, limitation on the image capturing operation is inconvenient to the user, for example, a long average total image capturing time or a complicated operating process, which even leads to an unsatisfactory final image.